ESA Summer of Code Project Proposal

Non-vacuum gravity simulator for the BRL-CAD Solid Modeling tool

About Myself

Name: Oana Niculaescu

Mailing List ID: oana.niculaescu@gmail.com

IRC ID: elf11

I am a student at the Polytechnic University of Bucharest, Romania, in the second year at the Computer Science faculty. I have a good background in programming and I had an internship with a local company here in Bucharest on game design and iOS. I also have a little bit of experience with CUDA and GPU programming. I am currently available for working 40 hours a week on this project. More details about my background are provided by my CV and I will link you my Github account, where some of my work is presented.

Brief project summary

The current non-vacuum gravity simulation available in BRL-CAD has not been developed to its fully potential and it is limited. My proposal is about continuing the work previously Abhijit Nandy did on the project and improve on his results. Since the Bullet Physics engine has been previously used and for this project and there are integrated tools for BRL-CAD, like gqa and rtcheck, that perform exact collision detection I consider there is no further need to switch to the Open Dynamics Engine (ODE). Basically the scene is read from a list of objects, the Bullet creates it and then forces are applied such that the position of the object will be updated, then the two BRL-CAD integrated tools for collision detection will be called and the collisions will be solved. Previously aligned axis bounding boxes have been used in collision detection and I consider it is a good thing to have a continuation with those.

Detailed project summary

Since the initial developer for this project has been intending on implementing a command in the Archer GUI for solving this problem, I will continue from where he left and will completely integrate the

Archer> run_simulation
command. The main work I am thinking to do will get done in the src/libged folder, the C++ code will get after integrated with the Tlc scripting language, that will call the C++ code for implementing a command. First I would further test the Sphere to Sphere collision and the collision pair generation logic. The btConvexConcaveCollisionAlgorithm, from the Bullet Physics Engine, supports collision between convex shapes and (concave) trianges meshes. This would be a nice addition to the BRL-CAD simulation. Also, in the same folder src/libged are functions that need to be ported to the src/librt level, the

that pass the color combination and apply it to a material, showing the current state of the object inside the physics engine. In the same folder there are some more functions that are not properly written and that need some additional work, like the function that gets the exact overlap volume between the 2 aligned axis bounding boxes and some more work on ray tracing.

Arbitrary collision detection and simulation will be the next milestone, in this section I think it would be proper to add some more physics specific attributes to the objects besides velocity that it is already there. I am thinking about gravity, friction force, some bouncing ball effect, like having a ball dropping on a hard surface and bouncing back in the air until it gets in a stable position. Here I will also add ground planes, materials which will be taking account of the surface of the ground. Currently only the bounding box is present in the implementation, but objects will get properties like elasticity and other custom forces. Integrating the Bullet btCylinderShape and completing the implementation of detecting collisions for arbitrary objects would be the next logical milestone.

After the primary physical forces are implemented, I will work on an improved gravitational system, where the gravity would depend mostly on the corps masses, bigger mass bigger gravity. For example if we have large objects dropping on the surface of a plane (e.g. Earth), there we will have to take into account the Earth gravity but also the pulling force that satellites (larger objects that gravitate around the Earth, like the Moon). I am thinking about implementing this as a command, in the archer GUI, after drawing the object the user can use a command similar to

set_objectMasses(Object *obj, type_t Value).

The function will be called and the pulling force, the gravity will be calculated considering the object masses.

Proposed Schedule

So far I have managed to compile and install BRL-CAD on a 64-bit Ubuntu 11.04 version. I am momentarily focusing on the “simulate” command in the archer, looking over the code Abhijit Nandy wrote for it. I have been going through the documentation/resources available on the brlcad.org/wiki.
I already have the Sourceforge and brlcad.org accounts. Now the proposed schedule, for the first month of the program, that I have come up with it is as follows :

adding the functionality of the btConvexConcaveCollisionAlgorithm, from the Bullet Physics Engine, to BRL-CAD, implementing concave-convex collision

Week 27th July – 3rd August

testing the new concave-convex collision with as many objects as possible

After this is done, further discussion with the mentoring organization will set the course of action that I must take.

Log

Here I will log the changes to the project as I will make them.

Expected result

The expected result is to allow the user to apply different forces to arbitrary objects and be able to simulate as accurate as possible the real world physics. The forces will be applied using an Archer GUI command and the user will be able to visualize the transformations the object is suffering in real time. Adding these facilities to the BRL-CAD program it will give the user the possibility to simulate a real world physics through the software.